A number of types of reciprocating power tools are in general use for various tasks, for example, saws, scrapers, hammers and the like. Commonly such tools are hydraulically or pneumatically powered; however, such power means necessitate the use of a noisy and bulky compressor or the like in conjunction with the tool itself, resulting in a limited range of utility of the tools, and such tools cannot easily or efficiently attain high speeds of reciprocation.
An alternative arrangement is to convert rotary movement provided by for example an electric motor into reciprocating movement of the tool bit. One means for achieving this conversion is to use the motor to drive the rotation of a cam bearing a sinusoidal cam track, and to provide the tool bit with a pair of cam followers which interact with the cam track. As the cam rotates, therefore, the cam followers will be driven forward and backward along the sinusoidal cam track, so driving the tool bit forward and backward. Such arrangements are described in previous patent applications GB 2 219 958A and W093/11910 by the same inventor, the contents of which are incorporated herein by reference.
While such arrangements have numerous advantages over pneumatically or hydraulically powered devices, it has until now been thought that provision of a sinusoidal cam track is an essential element of the invention.
International Patent Application WO93/23655 the contents of which are incorporated herein by reference, by the same inventor, describes a number of piston and cylinder devices wherein the piston is in the form of a cam member with a sinusoidal cam track in which are disposed a pair of fixed cam followers. Reciprocating movement of the piston (driven, for example, by combustion of a fuel in the chamber formed by the cylinder) is accompanied by a rotary motion imparted by the interaction of the cam followers and the cam track. The rotary motion may be used to drive an output member in a rotary action.
It is among the objects of embodiments of the present invention to obviate or alleviate disadvantages of the prior art.
It is further among the objects of embodiments of the present invention to provide a cam operated device which provides a greater acceleration of the member being driven on the forward and/or backward throw than that provided by prior art devices.
It is further among the objects of certain embodiments of the present invention to provide an electrically-driven reciprocating power tool which provides a greater impact velocity of the tool bit for a given power input than known electrically-driven reciprocating power tools.